Wednesday, October 16, 2019

Greenland's melting ice may affect everyone's future

Icebergs in Disko Bay, Greenland.
Photograph by Michael Melford, National Geo Image collection

From National Geographic by Alejandra Borunda

NASA scientists are trying to understand how this region is responding to climate change—and how that will influence sea levels around the world.

A thousand feet above the glistening, iceberg-dotted water of the ocean off of East Greenland, oceanographer Josh Willis braces for balance, his feet spread wide on the metal floor of a specially-outfitted airplane.
He grips a wide grey cylinder, hovering it over a 6-inch-wide bottomless tube.
The pilot’s voice crackles over the intercom: “3, 2, 1, zero, DROP.”
Willis lets the cylinder go.
With a whoosh, it slips down the tube and into the wide-open air.

The plane banks hard to the right and everyone on board rushes to a window.
“I see it!” yells Ian Fenty, another oceanographer on the project, as the probe—designed to sink to the seafloor and record the properties there—splashes down.

Willis, Fenty, and a crew of other scientists and pilots are flying the edge of Greenland’s vast ice sheet to figure out how the ocean eats away at the ice, speeding or slowing its slide into the water, where it melts, raising sea levels worldwide.

In an airplane flying low over the eastern coast of Greenland, Josh Willis, the lead scientist for the Oceans Melting Greenland (OMG) research project, prepares to drop a probe through a chute in the floor of a retrofitted DC-3 plane.
The probe will fly through through the air and land in the coastal ocean, where it will measure the temperature and salinity of the water.
photograph : Jonathan Nackstrand, AFP/Getty Images

But exactly how much ice it will deposit, and how fast, is still an open question.
Greenland is currently the biggest contributor to global sea level rise.
By 2100, will its ice sheet’s melt add inches to the world’s oceans—or will it add much more?

That’s a trillion-dollar question.
Nearly 70 percent of Earth’s population lives within 100 miles of a coast, and vast amounts of infrastructure—from airports to ports to cities to roads to Internet cables—sits in zones that could flood within decades.
Small, low-lying island nations, city planners, insurance adjustors, homeowners—everyone is clamoring for the most accurate estimates of how much extra water they’ll need to prepare for.

And for that, says Willis, they need to know what happens here, where ocean meets ice.
“This is where it all happens,” he says. The flooding of the future is being defined here and now, in the glittering sea below.

A sudden lurch into melting

Greenland’s ice is shrinking, this we've known for a while, since the science of global warming, a famous climate scientist likes to say, is older than the technology that makes our iPhones fast and the Internet run smoothly.

But until the 1990s, the ice in Greenland was remarkably stable, even as air temperatures rose because of human-caused climate change.
Each year, the ice sheet lost some weight as ice flowed like taffy from the center of the ice sheet, through funnel-like outlet glaciers at its edge, spilling into the ocean.
But enough snow fell on top of the mile-high interior of the ice sheet to balance out the losses.

In the 1990s, scientists thought that the big ice sheets in Greenland and Antarctica responded slowly to changes in climate, shuddering into motion like bears waking up from hibernation.
Yes, they’d respond to the human-caused climate change that was gripping the planet, the thinking went, but it would take decades or even centuries to really see the impacts.
“Early on, we weren’t thinking about Greenland as being really critical on these kind of decadal scales, and we didn’t have tools to look at them on those time scales,” explains Twila Moon, a glacier expert at the National Snow and Ice Data Center.

NASA's Oceans Melting Greenland (OMG) mission uses ships and planes to measure how ocean temperatures affect Greenland's vast icy expanses.
Jakobshavn Glacier, known in Greenlandic as Sermeq Kujalle, on Greenland's central western side, has been one of the island's largest contributor's to sea level rise, losing mass at an accelerating rate. In a new study, the OMG team found that between 2016 and 2017, Jakobshavn Glacier grew slightly and the rate of mass loss slowed down.
They traced the causes of this thickening to a temporary cooling of ocean temperatures in the region.

But around 1997, something changed.
Scientists studying Jakobshavn glacier, on Greenland’s western coast, watched in alarm as a tongue of ice that had for years poked out into a fjord started to shrink.
The tongue was about 15 kilometers long in 1997.
By the early 2000s—a scant half decade later—that tongue was gone.
“We suspected that this could happen from time to time, but this was the first time we’d seen anything like it,” says David Holland, who led the team studying the rapid disintegration of the ice tongue.

Huge chunks of ice break off the Jakobshavn glacier in Western Greenland.
Photo by James Balog, Nat Geo Image collection

Today, the Greenland ice sheet is losing mass about six times faster than it was just a few decades ago, whatever tenuous balance that existed before long since upended.
Between 2005 and 2016, melt from the ice sheet was the single largest contributor to sea level rise worldwide, though Antarctica may overtake it soon.

Within the past 50 years, the ice sheet has already shed enough to add about half an inch of water to the world’s oceans, and that number is increasing precipitously as the planet heats.
During this summer’s extreme heat wave that parked over Greenland for a week and turned over half its surface ice to slush, meltwater equivalent to over 4 million swimming pools sloughed into the ocean in a single day.
Over the month of July, enough melt poured into the ocean to bump sea levels up by an easily measurable half a millimeter.

Scientists at the University of Alaska Fairbanks’ Geophysical Institute used data from NASA’s Operation IceBridge to develop a more accurate model of how the Greenland Ice Sheet might respond to climate change in the future, finding that it could generate more sea level rise than previously thought.

Overall, there’s enough water locked up in the Greenland ice sheet to add about 25 feet to the world’s oceans.
It’s not likely that such catastrophic loss will happen soon, as in within the next few hundred years. But the whole of the ice sheet doesn’t have to collapse to cause massive, planet-wide reverberations.
“When I started this research, I never would have guessed that warm subsurface waters could unravel an ice sheet,” says David Holland, an oceanographer at NYU.
“But it’s becoming clear that they can, and that they are.”

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